Jet engine fan blade containment using an alternate geometry K.S. Carney a, * , J.M. Pereira a , D.M. Revilock a , P. Matheny b a NASA Glenn Research Center, 21000 Brookpark Road, Cleveland, OH 44135, USA b Florida Turbine Technology, West Palm Beach, FL, USA article info Article history: Received 5 November 2007 Received in revised form 8 August 2008 Accepted 3 October 2008 Available online 1 November 2008 Keywords: Containment Fan case Blade off Turbine engine Very high strain rate material behavior abstract With a goal of reducing jet engine weight, simulations of a fan blade containment system with an alternate geometry were tested and analyzed. A projectile simulating a fan blade was shot at two alternate geometry containment case configurations using a gas gun. The first configuration was a flat plate representing a standard case configuration. The second configuration was a flat plate with a radially convex curve section at the impact point. The curved surface was designed to force the blade to deform plastically, dissipating energy before the full impact of the blade is received by the plate. The curved case was able to tolerate a higher impact velocity before failure. The computational model was developed and correlated with the tests and a weight savings assessment was performed. For the particular test configuration used in this study the ballistic impact velocity of the curved plate was approximately 60 m/s (200 ft/s) greater than that of the flat plate. For the computational model to successfully duplicate the test, the very high strain rate behavior of the materials had to be incorporated. Published by Elsevier Ltd. 1. Introduction In order to insure passenger and crew safety, international aviation regulatory bodies, such as the Federal Aviation Adminis- tration in the United States and the Joint Aviation Authorities in Europe require that in commercial jet engines a system must exist which will not allow any compressor or turbine blade to perforate the engine case in the event that it is released from a disk during engine operation [1]. Due to this requirement the fan case is the heaviest single component of a jet engine. The Federal Aviation Administration further requires that jet engine manufacturers demonstrate, through a certification test, that the most critical blade be contained within the engine when a blade is released while the engine is running at full rated thrust [2]. The most critical blade in the engine, in terms of maximum kinetic energy, is invariably the fan blade, and the system designed to prevent it from penetrating the engine is called the fan containment system. The fan containment system includes a cylindrical case which surrounds the fan blades and disk. In modern high bypass turbine engines the fan blades are large and due to the large diameter of the fan section of the engine, the fan cases contribute significantly to overall engine weight. There are two general types of fan contain- ment systems, commonly referred to as hardwall and softwall systems. Hardwall systems consist of a relatively stiff section of the engine case that has sufficient strength to prevent perforation if impacted by a blade. Softwall systems usually consist of a relatively thin inner ring, surrounded by layers of dry fabric. Both systems include ribs and stiffeners which enhance system stiffness and both typically have generally flat cylindrical geometries. The geometry of the fan case can affect containment response. A careful selection of the geometry can improve containment and efficiency, allowing for case thickness reduction and reduced engine weight. The loss of blades in turbine engines, such as those shown in Fig. 1 , can be initiated by material failure due to fatigue, a bird strike [3], or some other foreign object damage. The fan blades are initially rotating at a very high rate, on the order of 5000 rpm. A released blade will attempt to follow a tangential trajectory, rotating about its center of gravity. That trajectory will cause the blade to impact the containment case at a relatively consistent angle and orientation. The character of a blade off impact, including point of impact, is surprisingly repeatable for an event which is triggered randomly. As a result, the blade off event may be tested and designed for in a deterministic manner. Future fan cases may incorporate an alternate geometry with a shallow convex curve in the radial direction of the cylindrical case as depicted in Fig. 2. As a released blade strikes the convex curve it will deform, dissipating its kinetic energy in plastic deformation before the full weight of the blade impacts. The proposal that the radially convex curved geometry will aid in containment was preliminarily explored using LS-DYNA [4] analysis. After showing promise in the preliminary analysis, ballistic tests on scaled, representative flat plates were performed to evaluate the concept. A final analysis was correlated with these tests, giving an estimate * Corresponding author. Tel.: þ1 216 433 2386. E-mail address: kelly.s.carney@nasa.gov (K.S. Carney). Contents lists available at ScienceDirect International Journal of Impact Engineering journal homepage: www.elsevier.com/locate/ijimpeng 0734-743X/$ – see front matter Published by Elsevier Ltd. doi:10.1016/j.ijimpeng.2008.10.002 International Journal of Impact Engineering 36 (2009) 720–728